Mental retardation (MR) is a lifelong disability which affects over six million individuals in the United States, including 2.5 million children ages 3-17 years. Only 45 percent of mild/moderate and 55 percent of severe/profound cases of mental retardation have known etiologies. Environmental contaminants such as mercury and polychlorinated biphenyls are known to have acute neurotoxic activity in utero, and the body of evidence suggests that moderate environment lead exposure is neurotoxic. The proposed project is an ecologic study of the correlation between environmental pollution measurements and the prevalence of mild/moderate, severe, and profound mental retardation in Alabama. Outcome measures will be obtained from the newly-established Mental Retardation Surveillance Dataset which contains the number of MR cases by age, race, level of disability, and county, from 1981-1993. Exposure measures will include data from the statewide pediatric lead screening program, the Toxic Release Inventory maintained by EPA, and air and water quality measurements collected by the Department of Environmental Management. These datasets will be linked at the level of the county, and correlational analysis will evaluate the association between MR prevalence and environmental contaminant distribution. Analysis will concentrate on those contaminants with known or suspected neurotoxic activity, and will control for potential confounders such as race, socioeconomic status, urbanization, and reproductive risk factors. Poisson regression analysis will be used to obtain risk ratios of MR for high versus low contaminant categories. The results from this study will be used to develop subsequent case-control and cohort studies of specific contaminant exposure-disability associations.